Research and Development in NiTi Shape Memory Alloys Fabricated by Selective Laser Melting
YANG Chao1(), LU Haizhou2(), MA Hongwei1, CAI Weisi1
1.National Engineering Research Center of Near-Net-Shape Forming for Metallic Materials, South China University of Technology, Guangzhou 510640, China 2.School of Mechatronic Engineering, Guangdong Polytechnic Normal University, Guangzhou 510665, China
Cite this article:
YANG Chao, LU Haizhou, MA Hongwei, CAI Weisi. Research and Development in NiTi Shape Memory Alloys Fabricated by Selective Laser Melting. Acta Metall Sin, 2023, 59(1): 55-74.
The postprocessing/machining of NiTi shape memory alloys (SMAs) is extremely challenging and difficult due to their low thermal conductivity and the high reactivity of ready-made NiTi parts. As a typical metal additive manufacturing technology, selective laser melting (SLM) offers significant advantages and can directly fabricate complex metallic parts, effectively address the problems of cold workability and machinability for NiTi parts. By establishing the relationship between processing parameters, microstructure, functional properties, and revealing the underlying mechanisms for altered phase transformation behavior and functional properties of SLM NiTi SMAs, it can serve as a theoretical foundation for expanding the applications of SLM NiTi SMAs. As a result, this paper comprehensively evaluates the formability, phase transformation behavior, microstructure, mechanical properties, and thermomechanical properties of SLM NiTi SMAs. Additionally, the design of SLM porous NiTi SMAs, as well as their biocompatibility, are discussed. Eventually, the future development trend and critical problems in studying SLM NiTi SMAs are investigated.
Fig.1 Research content and outline of selective laser melting (SLM) NiTi shape memory alloys (SMAs)
Fig.2 Feedstock powders to fabricate NiTi SMAs by SLM (a, b) pre-mixed Ni and Ti powders[21] (c) pre-alloyed Ni50.2Ti49.8 powder[22] (d-f) NiTi powders modified by Ni particles[23,24] (Inset in Fig.2d is particle size distribution of modified powders, and D50 is the average size of modified powders)
Process parameter
P / W
v / (mm·s-1)
h / mm
t / μm
E / (J·mm-3)
Ref.
characteristic
High P with high v
200-375
1000-1400
60
30
79-208
[26]
250
1250
120
30
55.5
[27-34]
200
1500
40-80
40
42-83
[35]
250
900-1100
60-75
30
123-126
[36]
250
1100
120
30
63
[37]
Low P with low v
50-120
100-300
45-150
20
55-675
[9]
70
105
100
30
222
[23]
120
250
50
40
240
[24]
40
160-280
50
30
95-111
[36]
60-120
150-600
75
30
44-267
[8,38]
90
600
90
30
56
[39]
120
500
80
30
110
[40-43]
90
414
120
30
61
[44]
70
80-300
100
30
78-292
[45-47]
50
200-300
120
30
46-69
[48]
60
300-480
110
25
46-73
[49,50]
50, 100
125
40-240
30
56-667
[51]
110, 120
150-350
50
30
210-533
[52]
Other
120
800
110
30
46
[53]
50-250
250-1250
80-120
30
40-125
[54]
75-200
400-1200
80-120
20-40
47-87
[55,56]
60-240
500
80
30
50-200
[57]
Table 1 Process parameters of SLM NiTi SMAs[8,9,23,24,26-57]
Fig.3 Variation of formability in SLM NiTi SMAs with different energy densities (low power and low scanning speed) (a)[9], SLM NiTi SMAs with different energy densities (high power and high scanning speed) (b)[26], diagrams between the process parameters of SLM Ni50.8Ti49.2 (c)[19] and Ni50.1Ti49.9 (d)[19] SMAs and formability predicted by Eagle-Tsai model (Pentagram shape in orange is SLM NiTi SMAs fabricated with low power and low scanning speed, pentagram shape in red is SLM NiTi SMAs fabricated with high power and high scanning speed)
Fig.4 Defects in SLM NiTi SMAs (a-d)[19] and effect of energy density on formability of SLM NiTi SMAs (e-h)[22]
Fig.5 DSC curves of SLM Ni50.6Ti49.4 with same energy density for as-fabricated (a)[10] and solution treated at 1000oC for 2 h (b)[10]; DSC curves of SLM Ni50.6Ti49.4 with altered laser power (c)[15]; DSC curves of as-fabricated (d)[35], solution treated (e)[35], and aged (f)[35] Ni51.4Ti48.6 fabricated with different hatches
Fig.6 TEM images of SLM Ni50.9Ti49.1 fabricated at different hatches showing subgrain structure and nanoprecipitates (a, c, e) and dislocations (b, d, f)[16] (a, b) center of the laser track at 35 μm hatch (c, d) center of the laser track at 120 μm hatch (e, f) edge of the laser track at 120 μm hatch
Fig.7 TEM images, STEM images, and selected area electron diffraction pattern of SLM NiTi alloys after heat treatment (a-d) TEM images of SLM Ni50.4Ti49.6 after solution treatment (at 1000oC for 1 h) and ageing (at 350oC/450oC for 1 h)[47] (e) STEM-HAADF image of SLM Ni51.4Ti48.6 after solution treatment (at 950oC for 12 h) and ageing (at 450oC for 5 h)[35] (f-h) STEM-HAADF image and selected area electron diffraction pattern of SLM Ni51.1Ti48.9 after ageing (at 400oC for 1 h)[19]
Fig.8 Summaries of mechanical properties of NiTi SMAs (a) NiTi SMAs by SLM[24,26,27,56,63-66], NiTi and NiTi-based composites by hot pressed sintering (HPS) and hot isostatic pressing (HIP)[67,68], and NiTi SMAs by selective electron beam melting[69] under compression (b) NiTi SMAs by SLM under tension[14,15,19,22,40-43,45,46,53,55,56,65,70-75]
Fig.9 Compression superelastic behaviors and cyclic superelastic behaviers of as-fabricated SLM NiTi SMAs (a) compression superelastic behaviors of Ni50.8Ti49.2 under the same energy density (55.5 J/mm3)[61] (Af—austenite transformation finish temperature) (b) compression superelastic behaviors of Ni50.8Ti49.2 under different laser scanning hatches[62] (c-f) cyclic superelastic behaviors of Ni50.8Ti49.2 under different laser powers and scanning speeds[62]
Fig.10 Compressive superelasticity of SLM NiTi SMAs (a) Ni50.8Ti49.2 in as-fabricated and different heat-treated states[29] (b) superelasticity of Ni50.8Ti49.2 in heat-treated at 350oC for 1 h[79] (c) single superelasticity of Ni51.4Ti48.6 in as-fabricated, solid solution, and ageing states[35] (σ—stress, ε—strain) (d-f) superelasticities of Ni51.4Ti48.6 in as-fabricated, solid solution, and ageing states during 10 cyc[35]
Fig.11 Uniaxial tensile mechanical properties and tensile superelasticity of SLM NiTi SMAs (a) uniaxial tensile mechanical properties of SLM Ni50.6Ti49.4 (at austenite state) at different laser powers[15] (b) uniaxial tensile mechanical properties of SLM Ni50.4Ti49.6 at martensite state[43] (c, d) tensile driving behaviors at different laser scanning hatches[80] (εact—actuation strain, εirr—irrecoverable strain) (e, f) cyclic tensile superelasticities of SLM Ni50.8Ti49.2 with and without heat treatment[19] (T—temperature) (g, h) cyclic tensile superelasticities of SLM Ni50.4Ti49.6 with different heat treatments[47]
NiTi (atomic
Feedstock
Equipment type
Compressive
Recovery
Cycle
Ref.
fraction / %)
stress
strain
number
MPa
%
Ni49.4Ti50.6 + Ni nanoparticles
Pre-alloyed powder
Concept Laser M2 Cusing
800
3.52-3.54
13
[23]
Ni53Ti47
Pre-alloyed NiTi powder (15-53 μm) +
Eplus-M100T
700-1800
4.0-9.4
4
[24]
coated Ni powder (1.5 μm)
Ni50.6Ti49.4
Pre-alloyed powder (15-53 μm)
An in-house SLM
800
5.6-6.7
10
[26]
machine (SLM-150)
Ni50.8Ti49.2
Pre-alloyed powder (25-75 μm)
3D Systems Phenix
1000
2.64-4.20
10
[29]
Ni51.4Ti48.6
Pre-alloyed powder (30-45 μm)
SLM-YZ250
600-850
2.2-4.6
10
[35]
Ni50.8Ti49.2
Pre-alloyed powder (D50 = 50 µm)
3D Systems Phenix PXM
800
2.23-4.56
10
[51]
Ni50.8Ti49.2
Pre-alloyed powder (25-75 μm)
3D Systems Phenix
800
2.29-5.50
10
[61]
Ni50.8Ti49.2
Pre-alloyed powder (25-75 μm)
3D Systems Phenix
600
3.40-5.20
10
[62]
Ni50.7Ti49.3
Pre-alloyed powder (D50 = 37 μm)
Solutions 280
700
3.7-7.4
10
[70]
Ni50.8Ti49.2
Pre-alloyed powder (D50 = 50 μm)
3D Systems Phenix
280-1750
1.5-5.5
4
[79]
Ni50.8Ti49.2
Pre-alloyed powder
Renishaw AM400
500/900
5.5/6
1
[82]
Ni50.8Ti49.2
Pre-alloyed powder (25-75 μm)
3D Systems Phenix PXM
300
3.0-3.4
1
[83]
Table 2 Recovery strains of SLM NiTi SMAs under compression[23,24,26,29,35,51,61,62,70,79,82,83]
NiTi (atomic
Feedstock
Equipment type
Tensile
Recovery
Cycle number
Ref.
fraction / %)
stress
strain
MPa
%
NiTi
Pre-alloyed powder
Eplus-M100T
500-700
1.41-2.14
10
[14]
(15-53 μm)
Ni51.1Ti48.9 and
Pre-alloyed powder
3D Systems ProX DMP 200
300-550
1.0-4.5
1 and incremental loading
[19]
Ni50.3Ti49.7
(D50 = 29 μm)
Ni51.2Ti48.8
Pre-alloyed powder
3D Systems ProX DMP 200
300-400
1-6
Incremental loading
[20]
Ni50.4Ti49.6
Pre-alloyed powder
Concept Laser M2 Cusing
450
0.77-2.31
20
[47]
(D50 = 37 μm)
Ni50.92Ti49.08
Pre-alloyed powder
Concept Laser Mlab-R
100-500
0.26-2.25
Incremental loading
[49]
(D50 = 40.6 μm)
Ni50.8Ti49.2
Pre-alloyed powder
BLT S210
400/500
2/4
1
[56]
(15-53 μm)
Ni50-51Ti49-50
Pre-alloyed powder
Renishaw AM400
300-550
2-4
8
[72]
Table 3 Recovery strains of SLM NiTi SMAs under tension[14,19,20,47,49,56,72]
Fig.12 Comparisons of mechanical properties of NiTi SMAs, stainless steel, and human tissues (a), isometric view of the CAD model and image of SLM porous Ni45.2Ti54.8 (b)[38], CAD models with three different pore sizes and image of SLM porous Ni50.4Ti49.6 (c)[63], cellular lattice structure and image of SLM porous Ni50.6Ti49.4 (d)[90], and CAD models and image of the SLM Ni50.3Ti49.7 gyroid cellular structure (e) (U-GCS: uniform gyroid cellular structure, Y-GCS: graded gyroid structure with the density gradient along y-axis, Z-GCS: graded gyroid structure with density along gradient z-axis)[37]
Fig.13 Mechanical properties of porous NiTi SMAs with different pore sizes (a)[63], mechanical properties of porous NiTi SMAs with different structures (b-d)[37], shape memory effect of porous NiTi SMAs with different pore sizes (εrec—recoverable strain) (e, f)[63], and superelasticities of porous NiTi SMAs with different strut thicknesses (g, h)[90]
Fig.14 Biocompatibility of SLM porous NiTi SMAs[63] (a) fluorescence images of live cell viability of MC3T3-E1 cells seeded on NiTi samples after being cultured for 1 d (The dotted circle and arrows indicate that MC3T3-E1 cells bridged the pores) (b, c) SEM images of MC3T3-E1 cells on outer (b) and inner (c) surfaces of the porous NiTi scaffolds after being cultured for 7 d in a humid environment at 37oC (The arrows indicate MC3T3-E1 cells)
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